Organic electro-luminescent display device and method of manufacturing the same

ABSTRACT

An organic electroluminescence device which includes a power line formed on the same layer as source and drain electrodes of a thin film transistor (TFT) and formed on a substrate on which the TFT is formed, a first insulating layer formed on the TFT, a lower electrode that electrically connected to one of the source and drain electrodes of the TFT and disposed on the first insulating layer, a first auxiliary power line and a second auxiliary power line formed on the same layer as the lower electrode in the second insulating layer, a second insulating layer formed on an edge portion of the lower electrode and not formed on the second auxiliary power line, wherein an opening that exposes a portion of the lower electrode is formed, an organic film formed on a substrate; and an upper electrode formed on the substrate.

CLAIM OF PRIORITY

This application claims the priority of Korean Patent Application No.10-2004-0009842, filed on Feb. 14, 2004, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescence displaydevice and a method of manufacturing the same, and more particularly, toan organic electroluminescence display device that can be formed with alarge size screen and can prevent non-uniform brightness of a panelusing an auxiliary power line to prevent a voltage drop of a power lineand an upper electrode and a method of manufacturing the same.

2. Description of the Related Art

Since organic electroluminescence display (OELD) devices are emissivedisplay devices that emit light by electrically exciting an organicfluorescent compound, can be driven at a low driving voltage, are slimand lightweight, and have a wide viewing angle and a quick responsetime, they are expected to solve the problems of and replace liquidcrystal display devices.

An OELD device generally includes an organic film (or layer) formed in apredetermined pattern and placed on a transparent insulating substrateformed of glass or other material and electrodes formed on and under theorganic film. The organic film is formed of an organic compound. In theabove structure of the OELD device, when a positive voltage and anegative voltage are applied to the electrodes, holes migrate to a lightemitting layer via a hole transport layer (HTL) from the electrode towhich the positive voltage is applied, electrons migrate to the lightemitting layer via an electron transport layer (ETL) from the electrodeto which the negative voltage is applied. Excitons are generated bycombining the holes and electrons in the light emitting layer and theexcitons change to a ground state while being excited. Thus, an image isformed by light emitted from fluorescent molecules of the light emittinglayer.

An active matrix (AM) organic electroluminescence display deviceincludes at least two thin film transistors (TFTs) in each pixel. TheTFTs are used as a switching device that controls the operation of thepixel and a driving device that drives the pixel. The TFTs have asemiconductor active layer having source and drain regions doped with ahigh concentration of dopant and a channel region formed between thesource and drain regions. The TFT is composed of a gate insulating layerformed on the semiconductor active layer, a gate electrode formed on thegate insulating layer on the channel region of the semiconductor activelayer, and, on the gate electrode, drain and source electrodes which areconnected to the source and drain regions via contact holes through aninter-insulator.

FIG. 1 is a plan view of a pixel of an AM OELD device, and FIG. 2 is across-sectional view of the pixel of FIG. 1.

Referring to FIG. 1, the AM OELD device includes a plurality ofsub-pixels. Each sub-pixel is arranged in a pixel region defined by ascan line (Scan), a data line (Data), and a driving line (VDD), and eachof the sub-pixels can be simply formed of at least two TFTs, such as aswitching TFT (TFTsw) and a driving TFT (TFTdr), one capacitor (Cst),and one organic light emitting diode (OLED). The numbers of TFTs andcapacitor are not limited to two and one, respectively, and more thantwo TFTs and more than one capacitor can be included.

The switching TFT (TFTsw) transmits data signals applied to the dataline Data by being driven by scanning signals applied to the scan line(Scan). The driving TFT (TFTdr) determines the amount of currentinputted to the OLED through the power line VDD according to the datasignals transmitted from the switching TFT (TFTsw), that is, a voltagedifference Vgs between the gate and the source. The capacitor (Cst)stores data signals transmitted through the switching TFT (TFTsw) duringone image frame.

FIG. 2 is a cross-sectional view of the pixel of FIG. 1. In FIG. 2, onlyan OELD and a TFT driving the OLED are illustrated.

Referring to FIG. 2, a buffer layer 110 is formed on a glass substrate100, and a TFT and an OLED are formed on the buffer layer 110.

A semiconductor active layer 121 is formed in a predetermined pattern onthe buffer layer 110 on the substrate 100. A gate insulating layer 130formed of SiO₂ is formed on the semiconductor active layer 121, and agate electrode 141 as a conductive film formed of MoW or Al/Cu is formedon the gate insulating layer 130. As depicted in FIG. 1, the gateelectrode 141 is connected to one of an upper or a lower electrode ofthe capacitor (Cst).

An inter-insulator 150 is formed on the gate electrode 141, and thesource and drain electrodes 161 are respectively connected to source anddrain regions (not shown) in the semiconductor active layer 121 viacontact holes. The power line VDD is also formed on the inter-insulator150 when the source and drain electrodes 161 are formed. A passivationfilm 170 formed of SiO₂ or SiNx is formed on the source and drainelectrodes 161 and a planarizing film 175 formed of an organic materialsuch as acryl, polyimide, or BCB is formed on the passivation film 170.

Via-holes 175 a and 170 a connected to the source and drain electrodes161 are formed in the passivation film 170 and the planarizing film 175by photolithography or perforation. A lower electrode layer 180 thatacts as an anode is formed on the planarizing film 175 and is connectedto the source and drain electrodes 161. A pixel defining layer 185formed of an organic material covering the lower electrode layer 180 isformed. After forming a predetermined opening in the pixel defininglayer 185, an organic layer 190 is formed in a region defined by theopening. The organic layer 190 includes a light emitting layer. Next, anupper electrode layer 195, which acts as a cathode is formed to coverthe organic layer 190. A portion of the organic layer 190 where thelower electrode layer 180 faces the upper electrode layer 195 emitslight by receiving holes and electrons.

Conventionally, in the AM OELD device, a transparent cathode is used foremitting light toward a direction of a sealed substrate. Generally, thetransparent cathode is formed of a transparent conductive material suchas ITO or IZO. However, to function as a cathode, after thinlydepositing a semitransparent metal film using a metal having low workfunction, such as MgAg, on a side that contacts the organic film, athick transparent conductive film formed of ITO or IZO is deposited onthe semitransparent metal film.

In a conventional method of manufacturing the OELD device, thetransparent conductive film is formed after forming the organic film190. At this time, the transparent conductive film is formed using a lowtemperature deposition process to minimize the damage of the organicfilm by heat or plasma. Therefore, the transparent conductive film haspoor film quality and has a high specific resistance.

When the specific resistance of a cathode is high, a non-uniform cathodevoltage can be applied to the pixels and can generate a voltagedifference between a location close to the power supply point and alocation remote from the power supply point due to a voltage drop. Thevoltage difference can cause non-uniform brightness and imagecharacteristics, and increases power consumption. The voltage drop isalso a reason that makes it difficult to manufacture a large size AMOELD device.

To solve this problem, Shoji Terada et al. have introduced a method offorming an auxiliary electrode for preventing a voltage drop of theupper electrode on a pixel defining layer 285 in 54.5L, SID2003 (Societyfor Information Display International Symposium, Seminar & Exhibition,Session 54, May 18-23, 2003, Baltimore, Md.). The OELD device depictedin FIG. 1 has a structure in which an auxiliary electrode line 193 forpreventing a voltage drop of the upper electrode is formed on the pixeldefining layer 185 and the upper electrode 195 that acts as a cathodeand is formed on an entire surface of the insulating substrate 100contacts the auxiliary electrode line 193.

However, the OELD device can solve the problem of non-uniform brightnesscaused by the voltage drop by forming the auxiliary electrode line 193but has drawbacks in that the organic film 190 can be damaged whenforming the auxiliary electrode line 193 by patterning after forming thesemitransparent metal film on the pixel defining layer 185. Also, thisprocess is complicated since a mask process for forming the auxiliaryelectrode line 193 is added.

On the other hand, the power line (VDD) that inputs a current to thesource and drain electrodes 161 is simultaneously formed and connectedto the source and drain electrodes 161 when forming the source and drainelectrodes 161. However, in the TFT structure, the wiring resistance ishigh due to a small cross-sectional area of the wiring since the wiringof the power line (VDD) is supplied from a side of the substrate.Therefore, the amount of current supplied to the driving TFT (TFTdr) isnon-uniform due to an RC delay and voltage drop resulting in thenon-uniform brightness of the OELD device.

As described above, due to the voltage drops in the power line (VDD) andcathode, the manufacturing of a large size AM OELD device is difficult.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved OELD device.

It is also an object of the present invention to provide a method ofmanufacturing the OELD device.

It is still an object of the present invention to provide an OELD devicethat prevents voltage drops of a power line (VDD) and a cathode using anauxiliary power line and a method of manufacturing the same.

It is further an object of the present invention to provide an OELDdevice that can be formed in a large size by improving imagecharacteristics and brightness thereof by preventing voltage drops of apower line (VDD) and a cathode and a method of manufacturing the same.

The above and other objects can be achieved by the present invention.

According to an aspect of the present invention, there is provided anOELD device comprising: a power line formed on the same layer as sourceand drain electrodes of a TFT and formed on a substrate on which the TFTis formed; a first insulating layer formed on the TFT; a lower electrodethat is electrically connected to one of the source and drain electrodesof the TFT and disposed on the first insulating layer; a first auxiliarypower line and a second auxiliary power line formed on the same layer asthe lower electrode; a second insulating layer formed on an edge portionof the lower electrode and not formed on the second auxiliary powerline, wherein an opening that exposes a portion of the lower electrodeis formed in the second insulating layer; an organic film formed on asubstrate; and an upper electrode formed on the substrate.

The first auxiliary power line is electrically connected to the powerline.

The first insulating layer is interposed between the first auxiliarypower line and the power line and the first auxiliary power line iselectrically connected to the power line through a via-hole formed inthe first insulating layer.

The second auxiliary power line is electrically connected to the upperelectrode. The second auxiliary power line is electrically connectedthrough a side surface to the upper electrode.

Preferably, the lower electrodes, the first auxiliary power line, andthe second auxiliary power line can be formed of the same material. Theycan be formed of a conductive material having a greater work functionthan a conductive material for forming the upper electrode, and morepreferably, can be formed of a material having a low specific resistanceand high reflectance.

The lower electrode, the first auxiliary power line, and the secondauxiliary power line can be formed as a single layer or a multiple layerand can be formed of Al-ITO, Mo-ITO, Ti-ITO, or Ag-ITO.

The lower electrode, the first auxiliary power line, and the secondauxiliary power line can have a greater thickness than the organic film.

The OELD device can include a plurality of sub-pixels having the TFTsand power lines, and one portion of the sub-pixels includes the firstauxiliary power line and the other portion of the sub-pixels includesthe second auxiliary power line.

Each of the first auxiliary power lines can be formed to cross the powerline of the sub-pixel which includes the first auxiliary power line.Also, each of the second auxiliary power lines can be formed to crossthe power line of the sub-pixel which includes the second auxiliarypower line. The first auxiliary power lines and the second auxiliarypower lines of the sub-pixels can be alternately formed.

According to another aspect of the present invention, there is providedan OELD device comprising: a power line formed on the same layer assource and drain electrodes of a TFT and formed on a substrate thatincludes the TFT; a first insulating layer formed on the TFT; a lowerelectrode that is electrically connected to one of the source and drainelectrodes of the TFT and disposed on the first insulating layer; afirst auxiliary power line and a second auxiliary power line formed onthe same layer as the lower electrode; a second insulating layer formedon an edge portion of the lower electrode and not formed on the secondauxiliary power line, wherein an opening that exposes a portion of thelower electrode is formed in the second insulating layer; an organicfilm formed on the lower electrode in the opening; and an upperelectrode formed on the substrate, wherein the second auxiliary powerline is electrically connected to the upper electrode through a sidesurface and an upper surface of the second auxiliary power line.

According to another aspect of the present invention, there is provideda method of manufacturing an OELD device comprising: forming a lowerelectrode electrically connected to one of source and drain electrodesof a TFT on a substrate that includes the TFT and a power line formed onthe same layer as the source and drain electrodes of the TFT and formingan auxiliary power line having a first auxiliary power line and a secondauxiliary power line formed on the same layer as the lower electrode;forming a pixel defining film that includes an opening for exposing aportion of the lower electrode and is formed on an edge portion of thelower electrode and not on the second auxiliary power line; forming anorganic film on the opening; and forming an upper electrode on thesubstrate.

The forming of the auxiliary power line includes: forming a planarizingfilm on the substrate that includes the TFT; forming a first via-holethat exposes the one of the source and drain electrodes of the TFT and asecond via-hole that exposes the power line in the planarizing film; andforming the lower electrodes electrically connected to the one of thesource and drain electrodes through the first via-hole and a firstauxiliary power line electrically connected to the power line throughthe second via-hole and a second auxiliary power line one theplanarizing film.

The first via-hole and a second auxiliary power line can be formed atthe same time. The lower electrode, the first auxiliary power line, andthe second auxiliary power line formed on the planarizing film may beformed of the same material.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention, and many of theabove and other features and advantages of the present invention, willbe readily apparent as the same becomes better understood by referenceto the following detailed description when considered in conjunctionwith the accompanying drawings in which like reference symbols indicatethe same or similar components, wherein

FIG. 1 is a plan view of a conventional front face emitting activematrix organic electroluminescence display (AM OELD) device;

FIG. 2 is a cross-sectional view of a pixel of FIG. 1;

FIG. 3 is a cross-sectional view showing structures of pixels arrangedin an nth column and (n+1)th column of an OELD device according to afirst embodiment of the present invention;

FIGS. 4A and 4B are cross-sectional views illustrating a method ofmanufacturing an OELD device according to an embodiment of the presentinvention;

FIGS. 5A and 5B are cross-sectional views illustrating a method ofmanufacturing an OELD device according to an embodiment of the presentinvention;

FIGS. 6A and 6B are cross-sectional views illustrating a method ofmanufacturing an OELD device according to an embodiment of the presentinvention;

FIGS. 7A and 7B are cross-sectional views illustrating a method ofmanufacturing an OELD device according to an embodiment of the presentinvention;

FIG. 8 is a cross-sectional view showing structures of pixels arrangedin an nth column and (n+1)th column of an OELD device according to asecond embodiment of the present invention; and

FIG. 9 is a plan view of an OELD device according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully with reference tothe accompanying drawings in which exemplary embodiments of theinvention are shown.

In the drawings and the specification, when a layer is shown ordescribed as placed on another layer or on a substrate in order toindicate that a layer is either directly formed upon the other layer oron the substrate, or, alternatively, that a layer is formed on a thirdlayer which, in turn, rests upon either the other layer or thesubstrate.

FIG. 3 is a cross-sectional view showing structures of pixels arrangedin an nth column and (n+1)th column of an OELD device according to afirst embodiment of the present invention.

Referring to FIG. 3, the OELD device according to a first embodiment ofthe present invention includes a buffer layer 210 formed on a substrate200, a thin film transistor (TFT) (hereinafter a first TFT) of a pixelarranged in an nth column and a TFT (hereinafter a second TFT) of apixel arranged in an (n+1)th column. The first and second TFTs aredisposed on the buffer layer 210. The substrate can be an insulatingsubstrate that includes glass or plastic or a metal substrate.

The first TFT includes a semiconductor active layer 221, a gateelectrode 241, source and drain electrodes 261, and the second TFTincludes a semiconductor active layer 222, a gate electrode 242, andsource and drain electrodes 262.

A gate insulating layer 230 is formed between the semiconductor activelayers 221 and 222 and the gate electrodes 241 and 242, and the sourceand drain electrodes 261 and 262 are formed on the inter-insulator 250and respectively connected to the semiconductor active layer 221 and 222through each contact hole. Also, power lines (VDD(n) and VDD(n+1)) areformed on the inter-insulator 250 at the same level as the source anddrain electrodes 261 and 262.

Each of the nth power line (VDD(n)) and the (n+1)th power line(VDD(n+1)) is connected in common to a plurality of pixels arranged in asame column, that is, the same data line. That is, as depicted in FIG.3, the nth power line (VDD(n)) is extended to connect in common to aplurality of pixels arranged in the nth column, and the (n+1)th powerline (VDD(n+1)) is extended to connect in common to a plurality ofpixels arranged in the (n+1)th column.

A passivation film 270 formed of SiO₂ or SiNx and a planarizing film 275formed of an organic film of acryl, polyimide, or BCB are formed on thesubstrate 200 on which the first and second TFTs are formed. A lowerelectrode 281 that acts as an anode of an OLED (a first OLED) of a pixelarranged in the nth column and a lower electrode 282 that acts as ananode of an OLED (a second OLED) of a pixel arranged in the (n+1)thcolumn are formed on the planarizing film 275. The lower electrode 281is electrically connected to one of the source and drain electrodes 261of the first TFT through via-holes 270 a and 275 a, and the lowerelectrode 282 is electrically connected to one of the source and drainelectrodes 262 of the second TFT through via-holes 270 c and 275 c.

Also, a first auxiliary power line (VDDa(n)) and a second auxiliarypower line (VSS(n+1)) are formed on the planarizing film 275 at the samelevel as the lower electrodes 281 and 282 of the first and second OLEDs.

The first auxiliary power line (VDDa(n)) is formed on the same layer asthe lower electrodes 281 and 282, and reduces the resistance of the nthpower line (VDD(n)) by electrically connecting to the nth power line(VDD(n)) through the via-holes 270 b and 275 b. In FIG. 3, for a betterunderstanding, the first auxiliary power line (VDDa(n)) is shown rotatedby 90 degrees. In fact, the first auxiliary power line (VDDa(n)) has astructure that extends along a scan line.

The second auxiliary power line (VSS(n+1)) is formed on the same levelas the lower electrodes 281 and 282, and reduces the resistance of theupper electrode 295 by electrically connecting to the upper electrode295. In FIG. 3, for a better understanding, the second auxiliary powerline (VSS(n+1)) is shown rotated by 90 degrees. In fact, the secondauxiliary power line (VSS(n+1)) has a structure that extends along thefirst auxiliary power line (VDD(n)).

A pixel defining film 285 is formed on a predetermined region includingan edge portion of the lower electrodes 281 and 282. The pixel definingfilm 285 is formed not to be disposed on the second auxiliary power line(VSS(n+1)). When patterning the pixel defining film 285, openings areformed by exposing portions of the lower electrodes 281 and 282. Theorganic film 290 is formed on the entire substrate or on the openings.As depicted in FIG. 3, in the present embodiment, the organic film 290is formed on the entire region on the substrate, but an organic film 290can be formed only on the openings as depicted in FIG. 8.

The organic film 290 is not formed on a side surface of the secondauxiliary power line (VSS(n+1)) but exposes the side surface of thesecond auxiliary power line (VSS(n+1)). An upper electrode 295 that actsas a cathode of the first and second OLEDs is formed on the organic film290. The organic film 290 is electrically connected to the side surfaceof the second auxiliary power line (VSS(n+1)) since the side surface ofthe second auxiliary power line (VSS(n+1)) is not covered by the organicfilm 290.

At this time, not to form the organic film 290 on side surfaces of thesecond auxiliary power line (VSS(n+1)), the organic film 290 is coatedafter forming the second auxiliary power line (VSS(n+1)) with athickness of greater than 3000 Å. The organic film 290 can be coated onthe pixel defining film 285 since the pixel defining film 285 is formedwith a certain taper angle. However, the side surfaces of the secondauxiliary power line (VSS(n+1)) are not completely covered by theorganic film 290 since the side surfaces of the second auxiliary powerline (VSS(n+1)) are formed almost vertically and much thicker than theorganic film 290.

The lower electrodes 281 and 282 that act as anodes, the first auxiliarypower line (VDDa(n)), the second auxiliary power line (VSS(n+1)) can beformed of the same material. Also, they can be formed of a conductivematerial having greater work function than a material for forming theupper electrode 295 that acts as a cathode, for example, after forming areflection film using Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or acompound of these metals, a transparent conductive film can be formed onthe reflection film using ITO, IZO, or In₂O₃. Preferably, the lowerelectrodes 281 and 282, the first auxiliary power line (VDDa(n)), andthe second auxiliary power line (VSS(n+1)) can be formed of a materialhaving a low specific resistance of 1 to 20 μΩcm for reducing thevoltage drop of the power line (VDD) and the cathode, and a materialhaving high reflectance of 70 to 99.9% for increasing the reflectance ofthe organic film 290 which will be formed in a subsequent process, suchas Al-ITO, Mo-ITO, Ti-ITO, or Ag-ITO or a material that can be used forforming a reflection film or an anode.

Also, the lower electrodes 281 and 282, the first auxiliary power line(VDDa(n)), and the second auxiliary power line (VSS(n+1)) can be formedas a single layer or a multiple layer.

The organic film 290 formed on the opening can be a low molecular weightorganic layer or a polymer layer. When the organic film 290 is a lowmolecular weight organic layer, the organic film 290 may be a holeinjection layer (HIL), a hole transport layer (HTL), an emission layer(EML), an electron transport layer (ETL), an electron injection layer(EIL) or a combination of these layers and can be composed of copperphthalocyanine (CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or tris-8-hydroxyquinoline aluminum (Alq3).The low molecular weight organic layer can be formed using anevaporation method.

If the organic film 290 is a polymer organic layer, the organic film 290can be an HTL and an EML. The HTL can be formed ofpoly-(2,4)-ethylene-dihydroxy thiophene (PEDOT) and the EML can beformed of a polymer such as Poly-Phenylenevinylene (PPV), orPolyfluorene and can be formed using a screen printing or an inkjetprinting.

The organic film is not limited thereto, but a variety of embodimentscan be applied.

The upper electrode 295 formed on the organic film 290 can be used as atransparent electrode or a reflection electrode. When the upperelectrode 295 is used as the transparent electrode since the upperelectrode 295 acts as a cathode, after depositing a metal layer using ametal having a low work function, such as Li, Ca, LiF/Ca, LiF/AI, Al,Mg, or a compound of these metals, a transparent electrode material canbe formed on the metal layer using ITO, IZO, ZnO or In₂O₃. When theupper electrode 295 is used as the reflection electrode, the upperelectrode 295 can be formed entirely depositing a metal layer using ametal having low work function, such as Li, Ca, LiF/Ca, LiF/AI, Al, Mg,or a compound of these metals. In the present embodiment, the upperelectrode 295 in the front face emitting OELD device can be formed byforming an IZO film on an MgAg metal layer having low work function andlow electrical resistance.

The upper electrode 295 is electrically connected to the side surfacesof the second auxiliary power line (VSS(n+1)) since the side surfaces ofthe second auxiliary power line (VSS(n+1)) are exposed, therebypreventing the voltage drop of the cathode.

FIG. 8 is a cross-sectional view showing structures of pixels disposedin an nth column and an (n+1)th column of an OELD device according to asecond embodiment of the present invention.

The AM OELD device depicted in FIG. 8 has a similar structure with theAM OELD device of the first embodiment. The difference between them isthat the organic film 290 in the first embodiment is formed on theentire surface of the substrate, and the upper electrode 295 iselectrically connected to the side surfaces of the second auxiliarypower line (VSS(n+1)), but an upper electrode 395 in the secondembodiment is electrically connected to the side surfaces and the uppersurface of the second auxiliary power line (VSS(n+1)) since an organicfilm 390 in the second embodiment is formed only on lower electrodes 381and 382 not on the second auxiliary power line (VSS(n+1)).

At this time, the organic film 390 can be formed only on the opening ofa pixel defining film 385 formed on an edge portion of the lowerelectrodes 381 and 382 by a method such as laser induced thermal imaging(LITI) transferring or patterning. That is, unlike in the firstembodiment, the organic film 390 is not formed on the second auxiliarypower line (VSS(n+1)).

Therefore, the voltage drop of the upper electrode 395 can be preventedby electrically connecting the upper electrode 395 to both side surfacesand the upper surface of the second auxiliary power line (VSS(n+1)) thatprevents the voltage drop of the upper electrode 395.

FIG. 9 is a plan view of an OELD device according to an embodiment ofthe present invention.

Referring to FIG. 9, an OELD device has a matrix shape of rows andcolumns having a plurality of sub-pixels, in which TFTs, lowerelectrodes, an organic layer, and an upper electrode are included.Conventionally, each pixel is composed of R, G, B sub-pixels, but is notnecessarily limited thereto. The sub-pixels in the same column areconnected to the same power line (VDD) and data line (Data). Thesub-pixels in the same row are connected to the same scan line (Scan).The sub-pixels in the same row are connected to a first auxiliary powerline (VDDa) or a second auxiliary power line (VSS), which is formed tocross the power line (VDD). The first auxiliary power line (VDDa) iselectrically connected to the power line (VDD) by the via-holes 270 band 275 b.

One portion of the sub-pixels are connected to the first auxiliary powerline (VDDa), and the other portion of the sub-pixels are connected tothe second auxiliary power line (VSS). In this manner, the sub-pixelsform a mesh shape.

In the embodiment depicted in FIG. 9, the first auxiliary power line(VDDa) and the second auxiliary power line (VSS) are alternately formedin each row. However, the number of the first auxiliary power lines(VDDa) can be increased if the voltage drop (IR drop) of the power line(VDD) is needed to be taken into consideration, and the number of thesecond auxiliary power lines (VSS) can be increased if the voltage dropof the cathode is needed to be taken into consideration.

A method of manufacturing an OELD device according to an embodiment ofthe present invention will now be described with reference to the FIGS.4A through 7B.

FIGS. 4A and 4B are cross-sectional views illustrating a method ofmanufacturing an OELD device, in which first and second TFTs and a powerline are formed on a substrate, according to an embodiment of thepresent invention.

A buffer layer 210 is formed on an insulating substrate formed of glassor plastic or a metal substrate. When the buffer layer 210 is formed,the penetration of impurity elements is prevented and a surface isplanarized. The buffer layer 210 can be formed of SiO₂ or SiN usingplasma enhanced chemical vapor deposition (PECVD), atmospheric pressurechemical vapor deposition (APCVD), low pressure chemical vapordeposition (LPCVD), or electron cyclotron resonance (ECR) in a thicknessof approximately 3000 Å. After forming semiconductor active layers 221and 222 on the buffer layer 210, ions are doped to the semiconductoractive layers 221 and 222. Afterward, a gate insulating layer 230 isformed on the semiconductor active layers 221 and 222 and gateelectrodes 241 and 242 are formed on the gate insulating layer 230.Next, source and drain electrodes 261 and 262 that contact thesemiconductor active layers 221 and 222 through via-holes are formed.This completes the manufacturing of the first and second TFTs.

More specifically, the semiconductor active layers 221 and 222 can beformed of an inorganic semiconductor or an organic semiconductor in athickness of approximately 500 Å. When the semiconductor active layers221 and 222 are formed of poly silicon of an inorganic semiconductor,after forming amorphous silicon, the amorphous silicon can becrystallized to a poly crystal by various crystallization methods. Theactive layer has source and drain regions highly doped with an N type ora P type dopant and a channel region is formed therebetween. Theinorganic semiconductor can be a silicon material including CdS, GaS,ZnS, CdSe, CaSe, ZnSe, CdTe, SiC, a-Si (amorphous silicon), or poly-Si(poly silicon), and the organic semiconductor can be a semiconductororganic material having a band gap in a range of 1-4 eV and can includea poly organic material such as polythiophene or a low molecular weightorganic material such as pentacene.

The gate insulating layer 230 formed of SiO2 is formed on thesemiconductor active layers 221 and 222, and the gate electrodes 241 and242 formed of a conductive metal, such as MoW, Al, Cr, or Al/Cu, areformed on a predetermined region on the gate insulating layer 230. Thematerial for forming the gate electrodes 241 and 242 are not limitedthereto, and they can be formed of various conductive materials such asconductive polymer. The region where the gate electrodes 241 and 242 areformed is a region corresponding to a channel region of thesemiconductor active layers 221 and 222.

An inter-insulator 250 formed of SiO₂ or SiNx is formed on the gateelectrodes 241 and 242, and the source and drain electrodes 261 and 262are formed on the inter-insulator 250 after forming a contact hole inthe inter-insulator 250 and the gate insulating layer 230. The sourceand drain electrodes 261 and 262 can be formed of a conductive metalfilm such as MoW, Al, Cr, or Al/Cu or a conductive polymer. The powerlines (VDD(n) and VDD(n+1)) are formed on the inter-insulator 250 at thetime the source and drain electrodes 261 and 262 are formed. The powerline (VDD) can be formed of the same material or a different materialfor forming the source and drain electrodes 261 and 262.

The structure of the TFT is not limited to the above descriptions. Theconventional TFTs can also be employed.

Next, referring to FIGS. 5A and 5B, the lower electrodes 281 and 282electrically connected to one of the source and drain electrodes 261 and262 of the TFTs are formed on the substrate 200 that includes TFTs andthe power line (VDD) formed on the same layer as the source and drainelectrodes 261 and 262 of the TFTs. The first and second auxiliary powerlines (VDDa and VSS) are formed on the same layer as the lowerelectrodes 281 and 282.

The first auxiliary power line (VDDa) is formed on the same layer as thelower electrodes 281 and 282, but it is electrically connected to thepower line (VDD(n)) through via-holes 270 b and 275 b. In FIG. 5A, for abetter understanding, the first auxiliary power line (VDDa(n)) is shownrotated by 90 degrees. In fact, the first auxiliary power line (VDDa(n))has a structure that extends along the scan line (Scan).

Also, in FIG. 5B, for a better understanding, the second auxiliary powerline (VSS(n+1)) is shown rotated by 90 degrees. In fact, the secondauxiliary power line (VSS(n+1)) has a structure that extends along thescan line (Scan).

The lower electrodes 281 and 282, the first auxiliary power line(VDDa(n)), and the second auxiliary power line (VSS(n+1)) are formed ona passivation film 270 and a planarizing film 275 coated on the TFT.

The passivation film 270 is formed of SiNx on the source and drainelectrodes 261 and 262, and the planarizing film 275 is formed of acryl,BCB, or polyimide on the passivation film 270. In a sub-pixel of the nthcolumn, via-holes 270 a and 275 a are formed in the passivation film 270and the planarizing film 275 to expose the source and drain electrodes261 and 262. Next, the lower electrode 281 of the first OLED is formedon the passivation film 270 and the lower electrode 281 is connected toone of the source and drain electrodes 261 through the via-holes 270 aand 275 a.

In a sub-pixel of the nth column, other via-holes 270 b and 275 b forexposing the power line (VDD(n)) are formed at the time when thevia-holes 270 a and 275 a are formed. The first auxiliary power line(VDDa(n)) is formed to be connected to the power line (VDD(n)) throughthe via-holes 270 b and 275 b at the same time when the lower electrode281 is formed on the planarizing film 275.

Also, via-holes 270 c and 275 c for exposing the source and drainelectrodes 262 are formed in a pixel of the (n+1)th column on thepassivation film 270 and the planarizing film 275 at the same time whenthe via-holes 270 a and 275 a are formed in a pixel of the nth column.Also, in the pixel of an (n+1)th column, the lower electrode 282 of thesecond OLED is formed in the pixel of an (n+1)th column, and the lowerelectrode 282 is connected to one of the source and drain electrodes 262through the via-holes 270 c and 275 c at the same time when the lowerelectrode 281 of the first OLED is formed on the planarizing film 275 ina pixel of the nth column. Also, the second auxiliary power line(VSS(n+1)) is formed on the power line (VDD(n+1)) in a sub-pixel of then+1th column at the same time when the lower electrodes 281 and 282 areformed on the planarizing film 275.

The lower electrodes 281 and 282 used as anodes, the first auxiliarypower line (VDDa), and the second auxiliary power line (VSS) can beformed of the same material, and can be formed of a conductive materialhaving a greater work function than a material for forming the upperelectrode 295 that acts as a cathode. For example, after forming areflection film using a metal such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd,Ir, Cr, or a compound of these metals, the lower electrodes 281 and 282,the first auxiliary power line (VDDa), and the second auxiliary powerline (VSS) can be formed by forming a layer using ITO, IZO, ZnO, orIn2O3 on the reflection film.

More preferably, the lower electrodes 281 and 282, the first auxiliarypower line (VDDa), and the second auxiliary power line (VSS) can beformed of a material having a low specific resistance for reducing thevoltage drop of the power line (VDD) and the upper electrode 295 whichacts as the cathode, and having high reflectance for increasing thereflectance of the organic film 290 which will be formed in a subsequentprocess, such as Al-ITO, Mo-ITO, Ti-ITO, or Ag-ITO or a material thatcan be used for forming a reflection film or an anode.

Also, the lower electrodes 281 and 282, the first auxiliary power line(VDDa), and the second auxiliary power line (VSS) can be formed as asingle layer or a multiple layer. The manufacturing process can bereduced by forming the lower electrodes 281 and 282, the first auxiliarypower line (VDDa(n)), and the second auxiliary power line (VSS(n+1)) atthe same time. The lower electrodes 281 and 282, the first auxiliarypower line (VDDa(n)), and the second auxiliary power line (VSS(n+1)) areformed as thick as possible so that the organic film 290, which will becoated on the second auxiliary power line (VSS(n+1)) in a subsequentprocess, can not cover side surfaces of the second auxiliary power line(VSS(n+1)). An upper electrode 295, which will be formed on the organicfilm 290 in a subsequent process, is electrically connected to thesecond auxiliary power line (VSS(n+1)) through the side surfaces of thesecond auxiliary power line (VSS(n+1)).

After forming the lower electrodes 281 and 282, the first auxiliarypower line (VDDa(n)), and the second auxiliary power line (VSS(n+1)), apixel defining film 285 is formed on edge portions of the lowerelectrodes 281 and 282 on the substrate 200. As depicted in FIGS. 6A and6B, the pixel defining film 285 is not formed on the second auxiliarypower line (VSS(n+1)). Openings that expose portions of the lowerelectrodes 281 and 282 are formed by forming the pixel defining film 285on edge portions of the lower electrodes 281 and 282.

Afterward, an organic film 290 that includes a light emitting layer iscoated on an entire surface of the insulating substrate 200. The organicfilm 290 is not formed on side surfaces of the second auxiliary powerline (VSS(n+1)). On the other hand, an upper electrode 295 that acts asa cathode of an OLED is formed on the organic film 290. The upperelectrode 295 is electrically connected to the second auxiliary powerline (VSS(n+1)) through the side surfaces of the second auxiliary powerline (VSS(n+1)) since the side surfaces of the second auxiliary powerline (VSS(n+1)) are not covered by the organic film 290.

At this time, the forming of the organic film 290 on the side surfacesof the second auxiliary power line (VSS(n+1)) can be avoided such thatthe organic film 290 is coated on the second auxiliary power line(VSS(n+1)) after forming the second auxiliary power line (VSS(n+1)) to athick thickness of greater than 3000 Å. The pixel defining film 285 isformed with a certain taper angle so that the organic film 290 can becoated, but the organic film 290 can not be formed on the side surfacesof the second auxiliary power line (VSS(n+1)) since the second auxiliarypower line (VSS(n+1)) is formed to a much greater thickness than thethickness of the organic film 290 and the side surfaces of the secondauxiliary power line (VSS(n+1)) is almost vertical.

Next, referring to FIGS. 7A and 7B, the upper electrode 295 that acts asa cathode is formed on an entire surface of the substrate 200. The upperelectrode 295 can be formed such that, after depositing a metal layerusing a metal having a low work function, such as Li, Ca, LiF/Ca,LiF/Al, Al, Mg, or a compound of these metals, toward the organic film290, a transparent electrode material, such as ITO, IZO, ZnO, or In₂O₃can be formed on the metal layer. In the present embodiment, the upperelectrode 295 can be formed by forming an IZO film on an MgAg metallayer having low work function and low electrical resistance.

The upper electrode 295 is electrically connected to the side surface ofthe second auxiliary power line (VSS(n+1)) by coating the upperelectrode 295. As described above, the upper electrode 295 can beelectrically connected to the second auxiliary power line (VSS(n+1))since the side surfaces of the second auxiliary power line (VSS(n+1)) isformed thick enough not to be covered by the organic film 290.

The embodiment depicted in FIG. 8 shows that the organic film 390 iscoated only on lower electrodes 381 and 382 and openings. Therefore, theside surfaces and an upper surface of the second auxiliary power line(VSS(n+1)) can contact the upper electrode 395. The rest of elements areidentical to the first embodiment.

FIG. 9 is a plan view of an OELD device according to an embodiment ofthe present invention. Referring to FIG. 9, an OELD device has a matrixshape of rows and columns having a plurality of sub-pixels in whichTFTs, the lower electrodes 281 and 282, the organic film 290, the upperelectrode 295 are included. The sub-pixels in the same column areconnected to the same power line (VDD) and data line (Data). Thesub-pixels in the same row are connected to the same scan line (Scan).The sub-pixels in the same row are connected to a first auxiliary powerline (VDDa) or a second auxiliary power line (VSS), which is formed tocross the power line (VDD). At this time, the first auxiliary power line(VDDa) is electrically connected to the power line (VDD) by thevia-holes 270 b and 275 b.

One portion of the sub-pixels are connected to the first auxiliary powerline (VDDa), and the other portions of the sub-pixels are connected tothe second auxiliary power line (VSS). In this manner, the sub-pixelsform a mesh shape on a plane.

In the present embodiment depicted in FIG. 9, the first auxiliary powerline (VDDa) and the second auxiliary power line (VSS) are alternatelyformed in each row. However, the number of the first auxiliary powerlines (VDDa) can be increased if the voltage drop (IR drop) of the powerline (VDD) is needed to be taken into consideration and the number ofthe second auxiliary power lines (VSS) can be increased if the voltagedrop of the cathode is needed to be taken into consideration.

As described above, according to the OELD device according to thepresent invention and the method of manufacturing the OELD device, thevoltage drop of the power line (VDD) and the voltage drop of the cathodecan be reduced at the same time by using a first auxiliary power lineand a second auxiliary power line. The non-uniform brightness and imagecharacteristics of the OELD device can be prevented by preventing thevoltage drop of the power line (VDD) and the voltage drop of thecathode.

A bus line for preventing the voltage drop can be formed, without anadditional masking process, by forming the first and second auxiliarypower lines at the time the anode is formed.

The present invention can provide an OELD device that has low powerconsumption and a large screen size by preventing the voltage drop ofthe power lines and the cathode, and can provide an improved lifetimeand reliable OELD device.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails, such as addition, deletion, modification, or revision ofelements that constitute the present invention, may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the following claims.

For example, although one TFT is depicted in the drawings, a pluralityof TFTs can be disposed on a practical plane according to a circuitdesign, the lower electrode can be used as an anode, the upper electrodecan be used as a cathode, the location of electrodes can be easilychanged, and therefore, all these modifications should considered within the scope of the present invention.

1. An organic electroluminescence display device, comprising: asubstrate; a thin film transistor formed on the substrate, said thinfilm transistor including source and drain electrodes; a power lineformed on the same layer as the source and drain electrodes of the thinfilm transistor and formed on the substrate; a first insulating layerformed on the thin film transistor; a lower electrode electricallyconnected to one of the source and drain electrodes of the thin filmtransistor and disposed on the first insulating layer; a first auxiliarypower line and a second auxiliary power line formed on the same layer asthe lower electrode; a second insulating layer formed on an edge portionof the lower electrode and not formed on the second auxiliary power lineto form an opening that exposes a portion of the lower electrode; anorganic film formed on the substrate; and an upper electrode formed onthe substrate.
 2. The organic electroluminescence display device ofclaim 1, wherein the first auxiliary power line is electricallyconnected to the power line.
 3. The organic electroluminescence displaydevice of claim 2, wherein the first insulating layer is interposedbetween the first auxiliary power line and the power line, and the firstauxiliary power line is electrically connected to the power line througha via-hole formed in the first insulating layer.
 4. The organicelectroluminescence display device of claim 1, wherein the secondauxiliary power line is electrically connected to the upper electrode.5. The organic electroluminescence display device of claim 4, whereinthe second auxiliary power line is electrically connected to the upperelectrode through a side surface of the second auxiliary power line. 6.The organic electroluminescence display device of claim 1, wherein thelower electrode, the first auxiliary power line, and the secondauxiliary power line are formed of the same material.
 7. The organicelectroluminescence display device of claim 6, wherein the lowerelectrode, the first auxiliary power line, and the second auxiliarypower line are formed of a conductive material having a greater workfunction than a conductive material for forming the upper electrode. 8.The organic electroluminescence display device of claim 6, wherein thelower electrode, the first auxiliary power line, and the secondauxiliary power line are formed of a material having a specificresistance of 1 to 20 μΩcm and reflectance of 70 to 99.9%.
 9. Theorganic electroluminescence display device of claim 6, wherein the lowerelectrode, the first auxiliary power line, and the second auxiliarypower line are formed as a single layer or a multiple layer.
 10. Theorganic electroluminescence display device of claim 6, wherein the lowerelectrode, the first auxiliary power line, and the second auxiliarypower line are formed of one selected from the group consisting ofAl-ITO, Mo-ITO, Ti-ITO, and Ag-ITO.
 11. The organic electroluminescencedisplay device of claim 6, wherein the lower electrode, the firstauxiliary power line, and the second auxiliary power line has a greaterthickness than the organic film.
 12. The organic electroluminescencedisplay device of claim 1, wherein the organic electroluminescencedisplay device includes a plurality of sub-pixels having the thin filmtransistor and the power lines, and one portion of the sub-pixelsincludes the first auxiliary power line and the other portion of thesub-pixels includes the second auxiliary power line.
 13. The organicelectroluminescence display device of claim 12, wherein each of thefirst auxiliary power lines is formed to cross the power line of thesub-pixel which includes the first auxiliary power line.
 14. The organicelectroluminescence display device of claim 12, wherein each of thesecond auxiliary power lines is formed to cross the power line of thesub-pixel which includes the second auxiliary power line.
 15. Theorganic electroluminescence display device of claim 12, wherein thefirst auxiliary power lines and the second auxiliary power lines of thesub-pixels are alternately formed.
 16. An organic electroluminescencedisplay device, comprising: a substrate; a thin film transistor formedon the substrate, said thin film transistor including source and drainelectrodes; a power line formed on the same layer as the source anddrain electrodes of the thin film transistor and formed on thesubstrate; a first insulating layer formed on the thin film transistor;a lower electrode electrically connected to one of the source and drainelectrodes of the thin film transistor and disposed on the firstinsulating layer; a first auxiliary power line and a second auxiliarypower line formed on the same layer as the lower electrode; a secondinsulating layer formed on an edge portion of the lower electrode andnot formed on the second auxiliary power line to form an opening thatexposes a portion of the lower electrode; an organic film formed on thelower electrode in the opening; and an upper electrode formed on thesubstrate, wherein the second auxiliary power line is electricallyconnected to the upper electrode through a side surface and an uppersurface of the second auxiliary power line.
 17. A method ofmanufacturing an organic electroluminescence display device, comprising:forming a lower electrode connected to one of source and drainelectrodes of a thin film transistor on a substrate that includes thethin film transistor and a power line formed on the same layer as thethin film transistor and the source and drain electrodes of the thinfilm transistor; forming an auxiliary power line comprising a firstauxiliary power line and a second auxiliary power line on the same layeras the lower electrode; forming a pixel defining film on an edge portionof the lower electrode and not on the second auxiliary power line toform an opening for exposing a portion of the lower electrode; formingan organic film on the opening; and forming an upper electrode on thesubstrate.
 18. The method of claim 17, wherein the forming of theauxiliary power line includes: forming a planarizing film on thesubstrate; forming a first via-hole that exposes the one of the sourceand drain electrodes and a second via-hole that exposes the power linein the planarizing film; and forming the lower electrode electricallyconnected to one of the source and drain electrodes through the firstvia-hole and the first auxiliary power line and the second auxiliarypower line electrically connected to the power line through the secondvia-hole on the planarizing film.
 19. The method of claim 18, whereinthe first via-hole and a second via-hole are formed at the same time.20. The method of claim 18, wherein the lower electrode, the firstauxiliary power line, and the second auxiliary power line formed on theplanarizing film are formed of the same material.
 21. The method ofclaim 18, wherein the lower electrode, the first auxiliary power line,and the second auxiliary power line formed on the planarizing film areformed of a conductive material having a greater work function than aconductive material for forming the upper electrode.
 22. The method ofclaim 18, wherein the lower electrode, the first auxiliary power line,and the second auxiliary power line formed on the planarizing film areformed of a material having a specific resistance of 1 to 20 μΩcm andreflectance of 70 to 99.9%.
 23. The method of claim 18, wherein thelower electrode, the first auxiliary power line, and the secondauxiliary power line are formed as a single layer or a multiple layer.24. The method of claim 18, wherein the lower electrode, the firstauxiliary power line, and the second auxiliary power line are formed ofone selected from the group consisting of Al-ITO, Mo-ITO, Ti-ITO, andAg-ITO.
 25. The method of claim 18, wherein the lower electrodes, thefirst auxiliary power line, and the second auxiliary power line has agreater thickness than the organic film.
 26. The method of claim 17,wherein the organic film is not formed on the side surfaces of thesecond auxiliary power line, and the second auxiliary power line iselectrically connected to the upper electrode through said side surfaceof the second auxiliary power line.
 27. The method of claim 17, whereinthe organic film is not formed on the side surfaces and the uppersurface of the second auxiliary power line, and the second auxiliarypower line is electrically connected through the side surface and theupper surface of the second auxiliary power line.
 28. The method ofclaim 17, wherein a plurality of sub-pixels having the first and secondauxiliary power lines are formed at the same time with the formation ofthe auxiliary power line, and the first auxiliary power line is formedon one portion of the sub-pixels and the second auxiliary power line isformed on the other portion of the sub-pixels.
 29. The method of claim17, wherein each of the first auxiliary power lines is formed to crossthe power line of the sub-pixel which includes the first auxiliary powerline.
 30. The method of claim 17, wherein each of the second auxiliarypower lines is formed to cross the power line of the sub-pixel whichincludes the second auxiliary power line.
 31. The method of claim 17,wherein the first auxiliary power lines and the second auxiliary powerlines of the sub-pixels are alternately formed.